This invention relates to a technique for fabricating a semiconductor integrated circuit device; and, more particularly, the invention relates to a technique that is applicable to the fabrication of a semiconductor integrated circuit device, including the step of polishing a thin film formed on the surface of a semiconductor wafer by a chemical mechanical polishing (CMP) method.
In the fabrication of a semiconductor integrated circuit device, an insulating film or dielectric film deposited on a silicon wafer is polished by a chemical mechanical polishing method to form an element isolation groove, to planarize an interlayer insulating film or to form a plug or a buried wiring.
In the conventional chemical mechanical polishing method, a polishing slurry is supplied on a lapping plate to which a pad made of a hard resin is attached, and the surface of a wafer is polished. As a polishing slurry, there is usually employed a slurry wherein fine particles of an abrasive, such as silica (silicon oxide), are dispersed in pure water, to which slurry an alkali for pH adjustment is added.
For silica in the polishing slurry, there is used a colloidal silica obtained by using sodium silicate as a starting material, or fumed silica obtained by combusting silicon tetrachloride (SiCL4) with an oxyhydrogen flame. The polishing slurry using the former colloidal silica has the problem that it contains sodium (Na) as an impurity. Although a colloidal silica is available whose content of sodium is reduced for overcoming the problem, such colloidal silica is inconveniently higher in production cost than the latter-mentioned fumed silica.
On the other hand, fumed silica is poorer than colloidal silica with respect to the dispersion stability in an aqueous dispersing medium. Accordingly, a problem has been indicated in the use of fumed silica in that, when a wafer is polished using a polishing slurry comprising this type of silica, the wafer surface suffers microscratches caused by coarse coagulations of the silica particles in the slurry. Many techniques for improving the dispersion stability of this type of slurry have been proposed.
It will be noted that the processes for preparing colloidal silica and fumed silica and the physical properties thereof are set out, for example, in Science of CPM, published on Jul. 19, 1999, by Science Forum Co., Ltd., pp. 128 to 142.
Japanese Laid-open Patent Application No. Hei 8(1996)-257 8 98 discloses an aqueous free grain slurry and its preparation. More particularly, abrasive particles, such as diamond, silicon carbide, alumina, silica, zirconia, cerium oxide, iron oxide, chromium oxide or the like, are applied on the surface thereof with plus charges from charge-determining ions, to which a surface active agent is attached so as to render the abrasive particles hydrophobic, thereby establishing a coagulated state. Eventually, the abrasive particles are prevented from settling with time, so that good dispersion stability and re-dispersability can be maintained over a long period of time.
Japanese Laid-open Patent Application No. Hei 11(1999)-246852 discloses a slurry for polishing and its preparation wherein the dispersability of abrasive grains is good. This slurry for polishing is made of a mixture of abrasive grains, an etching aqueous solution made of an alkaline or acidic aqueous solution having the ability of chemically etching a material to be polished, and a polymer material having a hydrophilic group, characterized in that the polymer material having a hydrophilic group is dispersed in the form of fine globules or is dissolved in the etching aqueous solution.
The abrasive grains used include those of oxides, sulfates or carbonates of silicon, aluminum, titanium, manganese, cesium, an alkaline earth metal or an alkali metal. The polymer material having a hydrophilic group includes a polyamide, a polyimide, a polyethylene, a polystyrene, a polyether, a polyurethane, a polycarbonate, a polyvinyl alcohol, a polyvinyl chloride or a polyvinylidene chloride, each having a carboxyl group, a hydroxyl group, a nitro group or an amino group.
With the slurry for polishing, the polymer material having a hydrophilic group is adsorbed on the abrasive grains, thereby imparting to the slurry thixotropic properties and the sedimentation-preventing function of the abrasive particles, under which the abrasive grains are mutually kept in a weakly coagulated state. Individual abrasive grains are kept in a well dispersed condition with the aid of the network structure through uniform secondary bonds of the molecules of the polymer material. As a result, the abrasive grains do not settle upon storage of the slurry; and, thus, the slurry can be used for polishing as it is without resorting to a procedure for recovering the dispersability by agitating the slurry again after long-term storage thereof.
Japanese Laid-open Patent Application No. Hei 10(1998)-193255 proposes a method of storing a slurry for polishing, which contains abrasive grains, such as of cesium oxide, alumina or manganese oxide, that are poor in dispersability in a liquid, so that when allowed to stand, they are coagulated with time and the polishing characteristics, such as the polishing rate or selection ratio of polishing, are changed in relation to time. In this storage method, after application of ultrasonic vibrations to the polishing slurry, the average size of the grains or a redox potential is measured so that the polishing rate is controlled by monitoring the average grain size or redox potential. It is stated that according to this method, because the degree of secular change in polishing rate of the polishing slurry can be confirmed, the polishing rate of the slurry under storage can be readily and reliably controlled, thus resulting in a great throughput and precise polishing.
In order to promote the scale down of elements and the formation of multi-layered wirings, a recent LSI is subjected to chemical mechanical polishing in a plurality of steps of a wafer process. For instance, in the step of forming an element isolation groove in the main surface of a wafer, the main surface of the wafer is dry etched using an oxidation-resistant film as a mask to form a groove in an element isolation region. Subsequently, a silicon oxide film is deposited on the main surface of the wafer, including the inside of the groove, to a thickness larger than the depth of the groove, followed by subjecting the silicon oxide film to chemical mechanical polishing by use of the oxidation-resistant insulating film as a stopper for polishing, thereby selectively leaving the silicon oxide film inside the groove to form an element isolation groove.
In such a chemical mechanical polishing step as set out above, it is usual to use a polishing slurry wherein silica particles are dispersed in water. Silica has a hydrophilic silanol group (Sixe2x80x94OH) on the surface thereof, so that when silica particles are dispersed in water, coagulation of particles (primary particles) takes place owing to the hydrogen bond among particles through the silanol group and the van der Waals force, thereby forming coagulated particles (secondary particles) having a size (i.e. diameter) larger than a single particle. Accordingly, the coagulated particles constitute a grain component in a polishing slurry where silica particles (dispersoid) are dispersed in water (dispersion medium).
When the coagulated particles are relatively small in size, little or no problem is involved. Nevertheless, an actual polishing slurry has coarse coagulated particles having a size of 1 pm or over (in this specification, coagulated particles having a size of 1 pm or over is especially called xe2x80x9ccoarse coagulated particles Such coarse coagulated particles cause fine defects, which are called micrO3cratche3, to occur on the surface of a wafer, thereby bringing about the lowerings of yield and reliability. For instance, in the step of forming such an element isolation groove as set out before, the silicon oxide film is subjected to chemical mechanical polishing by use of the oxidation-resistant insulating film as a stopper for the polishing. When microscratches are caused in the surface of the oxidation-reSi3tant insulating film, part of the microscratches reaches the underlying silicon substrate, thereby damaging the surface thereof.
For removing coarse coagulated particles from a slurry, a method of filtering the slurry is effective to an extent. Nonetheless, when the polishing slurry, from which the coagulated particles have been removed, is allowed to stand, coagulation takes place again, and thus, such a filtering method cannot be used as a fundamental measure.
In order to improve the dispersability of silica particles, it is effective to add a surface active agent to a polishing slurry. However, the use of a surface active agent needs an apparatus capable of coping with regulations on BOD and COD, and a measure against contamination with metallic ions in the surface active agent is also necessary. On the other hand, a method of agitating a polishing slurry prior to use has the possibility that foreign matter and coarse particles which have settled at the bottom of a slurry are undesirably included, and thus, this approach cannot be an effective measure against microscratches.
An object of the invention is to provide a technique for reducing the density of coagulated particles in a polishing slurry used in a chemical mechanical polishing procedure.
Another object of the invention is to provide a planarizing technique wherein microscratches can be reduced in number.
A further object of the invention is to provide a planarizing technique wherein a highly reliable integrated circuit can be formed.
A still further object of the invention is to provide a planarizing technique wherein the mass-production yield can be improved in a planarizing step in the production of a ULSI.
Another object of the invention is to provide a technique for control of a polishing slurry for planarization which is suited for mass-producing an integrated circuit device having a micro pattern.
The above and other objects and novel features of the invention will become apparent from the description provided in this specification when taken with reference to the accompanying drawings.
Typical embodiments of the invention are briefly summarized below.
(1) A method of fabricating a semiconductor integrated circuit device comprises the steps of:
(a) allowing a polishing slurry used for chemical mechanical polishing to stand so that a concentration of coagulated particles having a size of 1 xcexcm or over in the polishing slurry is at 200,000 particles/0.5 cc or below; and
(b) subjecting a surface to be processed of individual wafers running through a mass-production process to chemical mechanical polishing while supplying the polishing slurry obtained after the step (a) to the surface.
(2) A method of fabricating a semiconductor integrated circuit device comprises the steps of:
(a) allowing a polishing slurry used for chemical mechanical polishing to stand for 30 days or over; and
(b) subjecting a surface to be processed of individual wafers running through a mass-production process to chemical mechanical polishing while supplying the polishing slurry obtained after the step (a) to the surface.
(3) A method of fabricating a semiconductor integrated circuit device comprises the steps of:
(a) forming a groove in an element isolation region on a main surface of a wafer by etching the element isolation region on the main surface of the wafer by use, as a mask, of an oxidation-resistant insulating film formed on the main surface of the water;
(b) forming a silicon oxide insulating film on the main surface of the wafer including the inside of the groove; and
(c) subjecting the silicon oxide insulating film to chemical mechanical polishing through the oxidation-resistant insulating film as a stopper for polishing, so that the silicon oxide insulating film is selectively left inside the groove, thereby forming a polished, planarized insulating film isolation groove in the element isolation region on the main surface of the wafer, wherein, when the silicon oxide insulating film is subjected to chemical mechanical polishing, a polishing slurry obtained after being allowed to stand until a concentration of coagulated particles having a size of 1 xcexcm or over is at 200,000 particles/0.5 cc of the slurry or below is used.
(4) A method of fabricating a semiconductor integrated circuit device comprises the steps of:
(a) forming a groove in an element isolation region on a main surface of a wafer by etching the element isolation region on the main surface of the wafer by use, as a mask, of an oxidation-resistant insulating film formed on the main surface of the water;
(b) forming a silicon oxide insulating film on the main surface of the wafer including the inside of the groove; and
(c) subjecting the silicon oxide insulating film to chemical mechanical polishing through the oxidation-resistant insulating film as a stopper for polishing, so that the silicon oxide insulating film is selectively left inside the groove, thereby forming a polished, planarized insulating film isolation groove in the element isolation region on the main surface of the wafer, wherein, when the silicon oxide insulating film is subjected to chemical mechanical polishing, a polishing slurry obtained after being allowed to stand for 30 days or over is used.
In the practice of the invention, the term xe2x80x9cchemical mechanical polishing (CMP)xe2x80x9d refers to a manner of polishing where, while a polishing slurry is supplied, a surface to be polished is polished in contact with a polishing pad made of a relatively soft cloth-like sheet material by relative movement along the surface.
The term xe2x80x9cpolishing slurryxe2x80x9d means a suspension of a liquid colloidal state wherein fine particles of an abrasive (dispersoid) are suspended in water and a chemical etchant (dispersion medium). The term xe2x80x9cfine particles of an abrasivexe2x80x9d means fine particles of silica, ceria, zirconia, alumina or the like.
The term xe2x80x9callowing a polishing slurry to standxe2x80x9d is intended to mean that a polishing slurry is, placed in a container and allowed to stand in a still condition without subjecting it to vibrations, agitation, heating or the like. More particularly, the polishing slurry obtained, for example, by mixing fumed silica, pure water and an alkaline chemical solution and removing foreign matter therefrom is filled in an about 1 m square cubic container and stored in a storehouse whose temperature is maintained at a relatively uniform level. In this sense, to convey a polishing slurry after it has been filled in a container does not satisfy the requirement of xe2x80x9callowing to standxe2x80x9d or standing in the practice of the invention. For example, it is just as much conveying to ship a polishing slurry placed in a container (tank) via an ocean by means of a vessel as it is to transport it via a general road by means of a vehicle, such as a truck.
The term xe2x80x9cpolished, planarized insulating film isolation groovexe2x80x9d means an element isolation groove that is formed by selectively leaving, inside a groove, an insulating film whose surface is planarized by chemical mechanical polishing. Accordingly, an element isolation groove formed by merely depositing an insulating film inside the groove is different from the xe2x80x9cpolished, planarized insulating film isolation groovexe2x80x9d used herein. In other words, an element isolation groove generally called SGI (shallow groove isolation) or STI (shallow trench isolation) corresponds to the xe2x80x9cpolished, planarized insulating film isolation groovexe2x80x9d used herein.
In accordance with the present invention, the term xe2x80x9cmass-production process in a wafer linexe2x80x9d refers to a case where the throughput per day of a specific type of chemical mechanical polishing unit used in a wafer line is at least 25 wafers to 50 wafers or over, preferably 100 wafers or over, when calculated as an 8 inch square wafer.
As a matter of course, the limit number of wafers are in inverse proportion to the area of a water.
In the following embodiments, individual embodiments may be divided into a plurality of sections or embodiments for convenience""s sake, if necessary. Unless otherwise indicated, they are not mutually independent, but one may be in the relation of variations, details or a supplemental statement of part or the whole of others.
In the following embodiments, where reference is made to specific numbers or parameters of elements (including the number, value, amount, range and the like), such specific numbers or parameters should not be construed as limiting unless indicated so, and except in the case where limitation is apparent, principally placed on the specific numbers or parameters. The use of a larger or smaller number of intended elements may be within the scope of the invention. The elements or steps set out in the following embodiments are not always essential unless indicated so or except in the case where they are principally, apparently essential.
Likewise, where reference is made particularly to the shape, positional relationship of elements or members and the like in the following embodiments, a substantially similar or analogous shape or positional relationship is within the scope of the invention unless indicated so, or except in the case where it should not be principally, apparently included. This is true of the numerical values and ranges indicated in the present specification.
The term xe2x80x9csemiconductor integrated circuit devicexe2x80x9d used herein means not only those devices formed on a single crystal silicon substrate, but also those formed on other types of substrates including an SOI (silicon on insulator) substrate and a substrate for fabrication of a TFT (thin film transistor) liquid crystal unless otherwise indicated. The term xe2x80x9cwaferxe2x80x9d used herein means a single crystal silicon substrate (substantially in a disk form, in general), an SOI substrate, a glass substrate, other insulating, semi-insulating or semiconductor substrates, and combinations thereof.